Iran's former president, Akbar Hashemi Rafsanjani, announced last night he would stand in next month's presidential election.

In a written statement, Mr Rafsanjani called the decision "one of the most difficult of all my years of political activity", but said he was concerned by "the emergence of radical trends [in domestic politics]" and "sensitive regional and global conditions".

The announcement followed a day of frantic political speculation in Tehran, but came before a meeting scheduled between Mr Rafsanjani and Ayatollah Ali Khamenei, Iran's supreme leader.

An election where Iran's supreme leader backed a candidate against Mr Rafsanjani could be hazardous for the regime, which usually keeps serious differences behind closed doors.

Mr Rafsanjani apparently delayed his decision to stand out of fear of "character assassination" by militant conservatives, who resent his brand of conservative pragmatism and the way his supporters portray him as being the only candidate capable of dealing with the current international crisis surrounding Iran's nuclear programme.

The former president - in power from 1989 to 1997 - has faced growing criticism from Iran's hardline media, and eyebrows have been raised at the way Ayatollah Khamenei has apparently lent weight to the anti- Rafsanjani campaign.

But one official warned against being misled by appearances of differences between Mr Khamenei and Mr Rafsanjani. "The leader's relationship with [Mr] Rafsanjani is like marriage, or a love-hate relationship," he said. "If the country faces a crisis, the leader will accept Mr Rafsanjani standing."